U.S. patent number 7,987,731 [Application Number 12/521,443] was granted by the patent office on 2011-08-02 for ultrasonic flowmeter including an oscillation start unit for acceleration stability of the oscillator.
This patent grant is currently assigned to Panasonic Corporation. Invention is credited to Daisuke Bessyo, Fumikazu Shiba, Koichi Takemura.
United States Patent |
7,987,731 |
Bessyo , et al. |
August 2, 2011 |
**Please see images for:
( Certificate of Correction ) ** |
Ultrasonic flowmeter including an oscillation start unit for
acceleration stability of the oscillator
Abstract
The present invention provides an ultrasonic flowmeter
comprising an oscillator and an oscillation start unit for
accelerating oscillation of the oscillator. The oscillation start
unit accelerates the oscillation of the oscillator so that pulses
from the oscillator will become stable in a shorter time period.
The accuracy of flow rate measurement is improved. Electric power
can be saved where the flow rate is measured repeatedly at
intervals.
Inventors: |
Bessyo; Daisuke (Nara,
JP), Shiba; Fumikazu (Nara, JP), Takemura;
Koichi (Nara, JP) |
Assignee: |
Panasonic Corporation (Osaka,
JP)
|
Family
ID: |
39588298 |
Appl.
No.: |
12/521,443 |
Filed: |
April 26, 2007 |
PCT
Filed: |
April 26, 2007 |
PCT No.: |
PCT/JP2007/059117 |
371(c)(1),(2),(4) Date: |
June 26, 2009 |
PCT
Pub. No.: |
WO2008/081610 |
PCT
Pub. Date: |
July 10, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100319464 A1 |
Dec 23, 2010 |
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Foreign Application Priority Data
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Dec 27, 2006 [JP] |
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P2006-351251 |
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Current U.S.
Class: |
73/861.28 |
Current CPC
Class: |
G01F
1/667 (20130101) |
Current International
Class: |
G01F
1/66 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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51123044 |
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Oct 1976 |
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JP |
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54041058 |
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Mar 1979 |
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JP |
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08122117 |
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May 1996 |
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JP |
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09133562 |
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May 1997 |
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JP |
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2001320237 |
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Nov 2001 |
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JP |
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2003008403 |
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Jan 2003 |
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JP |
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2003315124 |
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Nov 2003 |
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JP |
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Other References
International Search Report for International Application No.
PCT/JP2007/059117, dated Jun. 26, 2007, 2 pages. cited by
other.
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Primary Examiner: Patel; Harshad
Attorney, Agent or Firm: Brinks Hofer Gilson & Lione
Claims
The invention claimed is:
1. An ultrasonic flowmeter comprising: an ultrasonic sensor that
sends and receives ultrasonic waves in a flow path; an oscillator
that generates an oscillation of a predetermined frequency; and an
oscillation start unit comprising an oscillation unit which outputs
pulses applied to the oscillator for a certain period to thereby
accelerate stability of the oscillator, wherein pulses of the
oscillator oscillated by the oscillation start unit are used to
measure a propagation time of the ultrasonic waves.
2. The ultrasonic flowmeter as claimed in claim 1, wherein a
driving signal is given to the ultrasonic sensor in synchronization
with pulses of the oscillator oscillated by the oscillation start
unit and a waiting period is provided before the driving signal is
given to the ultrasonic sensor after the oscillator becomes
oscillated by the oscillation start unit.
3. The ultrasonic flowmeter as claimed in claim 2, wherein the
waiting period is set at a constant time.
4. The ultrasonic flowmeter as claimed in claim 2, wherein the
waiting period is determined based on a result of verifying the
pulse cycle of the oscillator.
5. The ultrasonic flowmeter as claimed in claim 1, wherein a
ceramic oscillator is used in the oscillator.
6. The ultrasonic flowmeter as claimed in claim 5, further
comprising another oscillator in addition to the oscillator,
wherein a pulse cycle of the oscillator is verified by pulses of
said another oscillator to correct the measured propagation
time.
7. The ultrasonic flowmeter as claimed in claim 6, wherein the
pulse cycle of the oscillator is verified continuously the
propagation time is measured.
8. An ultrasonic flowmeter comprising: an ultrasonic sensor that
sends and receives ultrasonic waves in a flow path; an oscillator
that generates an oscillation of a predetermined frequency; and an
oscillation start unit that accelerates stability of the
oscillator, wherein a driving signal is given to the ultrasonic
sensor in synchronization with pulses of the oscillator oscillated
by the oscillation start unit to use pulses of the oscillator
oscillated by the oscillation start unit to measure a propagation
time of the ultrasonic waves, and a waiting period is provided
before the driving signal is given to the ultrasonic sensor after
the oscillator becomes oscillated by the oscillation start unit.
Description
TECHNICAL FIELD
The present invention relates particularly to an ultrasonic
flowmeter for measuring a flow rate by ultrasonic waves.
BACKGROUND ART
A conventional ultrasonic flowmeter is described in, for example,
Patent Reference 1. FIG. 6 is a control block diagram showing a
first example of the conventional ultrasonic flowmeter described in
Patent Reference 1.
In the ultrasonic flowmeter of FIG. 6, a first oscillator 5 for
sending ultrasonic waves on the way to a fluid pipe line 4 and a
second oscillator 6 for receiving the ultrasonic waves are arranged
in a flow direction. Also, the ultrasonic flowmeter comprises a
sending circuit 7 to the first oscillator 5, and an amplification
circuit 8 of a signal received by the second oscillator 6. Then,
the ultrasonic flowmeter has a configuration in which a signal
amplified by the amplification circuit 8 is compared with a
reference signal by a comparison circuit 9 and time from sending to
receiving is obtained by a time counting unit 10 such as a timer
counter and a flow rate value is obtained by a flow rate
calculation unit 11 in consideration of a state of a flow or a size
of the pipe line according to its ultrasonic propagation time and
timing of signal sending to a trigger unit 13 of the sending
circuit 7 is adjusted by a value of this flow rate calculation unit
11.
Next, its operation will be described. A burst signal is sent out
of the sending circuit 7 based on instructions from the trigger
unit 13 and an ultrasonic signal sent by the first oscillator 5
according to this burst signal propagates through a flow and is
received by the second oscillator 6. Then, the received signal is
processed by the amplification circuit 8 and the comparison circuit
9 and time from sending to receiving is measured by the time
counting unit 10.
When a sound in static fluid is set at c and a speed of a fluid
flow is set at v, an ultrasonic propagation speed of a forward
direction of the flow becomes (c+v). When a distance between the
oscillators 5 and 6 is set at L and an angle between the ultrasonic
propagation axis and the central axis of a pipe line is set at
.phi., ultrasonic arrival time T is as follows, T=L/(c+v COS .phi.)
(1) and the following formula is obtained from the formula (1),
v=(L/T-c)/COS .phi.) (2) and when L and .phi. are known, a flow
speed v is obtained by measuring T. From this flow speed, a flow
rate Q is obtained by the following formula when a passage area is
set at S and a correction factor is set at K. Q=KSv (3)
FIG. 7 is a control block diagram showing a fourth example of the
conventional ultrasonic flowmeter described in Patent Reference 1.
In the ultrasonic flowmeter of FIG. 7, repeats of sending to
receiving are done by the number of repeats set in a repeat setting
unit 16 by a repeat unit 15 and switching between sending and
receiving is further performed by a switching unit 17 and
thereafter, repeats are similarly done. That is, when ultrasonic
waves are generated from a first oscillator 4 by a sending circuit
7 and the ultrasonic waves are received by a second oscillator 5
and a received signal arrives at a comparison circuit 9 through an
amplification circuit 8, the sending circuit 7 is again triggered
by a trigger unit 13 by instructions of the repeat unit 16. This
repeat is done by the number of repeats set in the repeat setting
unit 15 and when the number of set repeats is reached, time taken
to do the repeats is measured by the time counting unit 10.
Thereafter, sending and receiving of the first oscillator 4 and the
second oscillator 5 are connected in reverse by the switching unit
17 and in turn, ultrasonic waves are sent from the second
oscillator toward the first oscillator 5 and in a manner similar to
the above, arrival time is obtained and this difference is obtained
and a flow rate value is calculated by the flow rate calculation
unit 11.
When a sound in static fluid is set at c and a speed of a fluid
flow is set at v, an ultrasonic propagation speed of a forward
direction of the flow becomes (c+v) and a propagation speed of a
backward direction becomes (c-v). When a distance between the
oscillators 7 and 8 is set at L and an angle between the ultrasonic
propagation axis and the central axis of a pipe line is set at 4)
and the number of repeats is set at n, respective repeat times T1
and T2 of the forward direction and the backward direction are as
follows, T1=n.times.L/(c+v COS .phi.) (4) T2=n.times.L/(c-v COS
.phi.) (5) and the following formula is obtained from the formulas
(4) and (5), v=n.times.L/2COS .phi..times.(1/T1-1/T2) (6) and when
L and .phi. are known, a flow speed v is obtained by measuring T1
and T2.
However, when a flow rate is small and the number of repeats is
small, a difference between T1 and T2 is extremely minute and it is
difficult to accurately measure the difference, so that the number
of measurements is largely set and an error is relatively
decreased. Also, when the flow rate becomes large, the difference
of T1-T2 also becomes large, so that it becomes easy to measure the
difference and in that case, the number of repeat settings is
decreased and a sampling interval is quickened and the error is
decreased. That is, the number of repeats of the repeat setting
unit 15 is changed by the flow rate calculation unit 11.
The ultrasonic flowmeter of this Patent Reference 1 has a method
for switching between sending and receiving using two oscillators
and obtaining a flow speed from ultrasonic propagation times
obtained from respective received waveforms and calculating a flow
rate. Patent Reference 1: JP-A-8-122117
DISCLOSURE OF THE INVENTION
Problems that the Invention is to Solve
Measurement of propagation time of ultrasonic waves is obtained by
counting the number of pulses generated by an oscillator as an
oscillation element. For example, in the case of using a crystal
oscillator with 4.times.10.sup.6 Hz (a cycle is the reciprocal of a
frequency and is 0.25.times.10.sup.-6 second) as the oscillator,
propagation time becomes 180.times.10.sup.-6 second when there are
720 pulses in the propagation time. The crystal oscillator becomes
a measurable state after the crystal oscillator oscillates from an
operation start of a circuit to which its crystal oscillator is
connected and an amplitude of oscillation increases and a clear
pulse waveform is obtained and time taken to stabilize this pulse
cycle or duty has elapsed.
This respect will be described using the drawings. When a waveform
is measured using a product number SMD49TA4M (for 4.times.10.sup.6
Hz) of a crystal oscillator made by Daishinku Corporation as an
oscillator 70 in an oscillation circuit of FIG. 8, a waveform
diagram of FIG. 9 is obtained. The axis of abscissa of FIG. 9 is
time (second), and (a) in FIG. 9 shows a power source voltage
supplied to a circuit, and increases slowly in order to charge a
capacitor inserted for voltage stabilization. In the case of
reaching a voltage on which a buffer 71 (TC74HC04 made by Toshiba
Corporation) and an unbuffer 72 (TC74HCU04 made by Toshiba
Corporation) of a circuit can operate, an output voltage V1 of the
unbuffer 72 (TC74HCU04) of (b) in FIG. 9 appears and an amplitude
of its oscillation increases gradually. This voltage V1 is inputted
to the buffer 71 (TC74HC04) and when V1 exceeds a threshold voltage
of this buffer 71, an output voltage V2 of a rectangular wave is
outputted from the buffer 71 at time T.sub.CR1=4.times.10.sup.-3
second as shown in FIG. 9, (c). Some time T.sub.CR2 taken to
stabilize a cycle of this rectangular wave after the output voltage
V2 of the rectangular wave is outputted is required.
FIG. 10 is a graph showing a change in a cycle of this rectangular
wave after the output voltage V2 of the rectangular wave is
outputted, and the axis of abscissa is time (second) and the axis
of ordinate is a pulse cycle (second). In the case of seeing this
FIG. 10, time T.sub.CR2 necessary to stabilize the cycle at
0.25.times.10.sup..about.6 second is about 1.times.10.sup..about.3
second.
As a result of this, it is necessary to previously start up a
crystal oscillator before measurement of propagation time of
ultrasonic waves is started. This time is T.sub.CR1+T.sub.CR2 and
requires about 5.times.10.sup..about.3 second. In an ultrasonic
flowmeter using a battery as an electric power source, electric
power savings are strongly desired. As a result of this, in the
measurement of propagation time of ultrasonic waves, control made
by intermittent measurement every, for example, 4.times.10.sup.-3
second is performed.
However, when the crystal oscillator is used in measurement of
propagation time of ultrasonic waves, stability of a pulse capable
of being used in measurement cannot be obtained unless the crystal
oscillator is started up before 5.times.10.sup.-3 second capable of
being used in measurement as described above. Therefore, when
measurement intervals are 4.times.10.sup.-3 second, the crystal
oscillator cannot be stopped and it becomes necessary to
continuously operate the crystal oscillator. Since power
consumption by a circuit for operating the crystal oscillator is
large, a continuous operation of the crystal oscillator becomes a
problem in the case of achieving electric power savings.
The oscillator includes a ceramic oscillator in addition to the
crystal oscillator. Activation of the ceramic oscillator is quicker
than that of the crystal oscillator. When a waveform is measured
using a product number EFOMC400AR (for 4.times.10.sup.6 Hz) of the
ceramic oscillator made by Matsushita Electric Industrial Co., Ltd.
as an oscillator 73 in an oscillation circuit of FIG. 11, a
waveform diagram of FIG. 12 is obtained. The axis of abscissa of
FIG. 12 is time (second), and (a) in FIG. 12 shows a power source
voltage supplied to a circuit, and increases slowly in order to
charge a capacitor inserted for voltage stabilization. In the case
of reaching a voltage on which a buffer 71 and an unbuffer 72 of a
circuit can operate, oscillation appears in an output voltage V1 of
the unbuffer 72 of (b) in FIG. 12 and an amplitude of its
oscillation increases gradually. This voltage V1 is inputted to the
buffer 71 and when V1 exceeds a threshold voltage of this buffer
71, an output voltage V2 of a rectangular wave is outputted from
the buffer 71 at time T.sub.CE1=44.times.10.sup.-6 second as shown
in FIG. 12 (c). Some time T.sub.CE2 taken to stabilize a cycle of
this rectangular wave after the output voltage V2 of the
rectangular wave is outputted is required.
FIG. 13 is a graph showing a change in a cycle of this rectangular
wave after the output voltage V2 of the rectangular wave is
outputted, and the axis of abscissa is time (second) and the axis
of ordinate is a cycle (second). In the case of seeing this FIG.
13, time T.sub.CE2 necessary to stabilize the cycle at
0.25.times.10.sup.-6 second is about 5.times.10.sup.-5 second.
As a result of this, it is necessary to previously start up the
ceramic oscillator before measurement of propagation time of
ultrasonic waves is started. This time is T.sub.CE1+T.sub.CE2 and
requires about 9.4.times.10.sup.-5 second. The extent of this
stability is the extent of stability determined from ambient
environment or a measuring device for measuring a cycle in the same
experiment. In the case of making actual measurement of propagation
time of ultrasonic waves using the ceramic oscillator and then
calculating a flow rate, a standard deviation of the flow rate is
shown in FIG. 14 when waiting time taken to start measurement after
a power source of an oscillation circuit of the ceramic oscillator
is turned on is obtained as a parameter. As can be seen from FIG.
14, the standard deviation of the flow rate becomes small at about
200.times.10.sup.-6 second or more and is stable.
Thus, when the ceramic oscillator is used as the oscillator,
activation of the oscillator becomes extremely quicker than that of
the crystal oscillator, but about 200.times.10.sup.-6 second or
more is required still, so that a problem is to accelerate stable
oscillation and activation of the ceramic oscillator further in
order to achieve electric power savings.
Also, in consideration of a change in working temperature range or
variations between individual pieces, oscillation frequency
accuracy of the crystal oscillator is .+-.0.001% but oscillation
frequency accuracy of the ceramic oscillator is .+-.0.5% and there
is a problem in absolute time accuracy in the case of using the
ceramic oscillator.
Means for Solving the Problems
An ultrasonic flowmeter of the invention uses an oscillation start
unit in order to accelerate an oscillation start of an oscillator
used in measurement of propagation time of ultrasonic waves and
enhance stability of an oscillation pulse. The oscillation start
unit comprises an oscillation circuit for generating a pulse of a
frequency close to an oscillation frequency of the oscillator used
in measurement, and the oscillator used in measurement of
propagation time of ultrasonic waves is energized by the pulse
generated by its oscillation circuit.
We confirmed that such oscillation start unit not only accelerates
an oscillation start of an oscillator but also accelerates time for
which a frequency (cycle) of oscillating pulses is stabilized, and
confirmed that sufficient flow rate measurement accuracy and
electric power savings can be achieved when this oscillation start
unit is applied to the ultrasonic flowmeter and a flow rate is
measured.
Also, we use a ceramic oscillator in an oscillator used in
measurement of propagation time of ultrasonic waves to solve low
oscillation frequency accuracy of the ceramic oscillator. For this
purpose, it is constructed so that a crystal oscillator oscillating
at a frequency lower than that of the ceramic oscillator used in
the measurement of propagation time is disposed and a pulse cycle
of the ceramic oscillator is verified by a pulse of the crystal
oscillator oscillating at the lower frequency to calibrate the
propagation time. Concretely, the actual ultrasonic flowmeter is
equipped with a circuit for measuring ultrasonic waves and a
microcomputer for controlling this circuit and controlling flow
rate display etc., and the microcomputer operates always and as an
oscillator for operating this, for example, a crystal oscillator
with 32.times.10.sup.3 Hz is used. Hence, using this crystal
oscillator with 32.times.10.sup.3 Hz, a ceramic oscillator with
4.times.10.sup.6 Hz for measuring ultrasonic waves is verified to
calibrate the propagation time.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit block diagram showing a structure of an
ultrasonic flowmeter of the invention.
FIG. 2 is a timing chart of the ultrasonic flowmeter of the
invention.
FIG. 3 is a circuit block diagram showing a structure of an
ultrasonic flowmeter of the invention.
FIG. 4 is a timing chart of the ultrasonic flowmeter of the
invention.
FIG. 5 is a timing chart of an ultrasonic flowmeter of the
invention.
FIG. 6 is a control block diagram showing a configuration of a
conventional ultrasonic flowmeter.
FIG. 7 is a control block diagram showing a configuration of a
conventional ultrasonic flowmeter.
FIG. 8 is an oscillation circuit of a conventional crystal
oscillator.
FIG. 9 is a characteristic diagram of the oscillation circuit of
the conventional crystal oscillator.
FIG. 10 is a characteristic diagram of the oscillation circuit of
the conventional crystal oscillator.
FIG. 11 is an oscillation circuit of a conventional ceramic
oscillator.
FIG. 12 is a characteristic diagram of the oscillation circuit of
the conventional ceramic oscillator.
FIG. 13 is a characteristic diagram of the oscillation circuit of
the conventional ceramic oscillator.
FIG. 14 is a flow rate characteristic diagram measured using the
oscillation circuit of the conventional ceramic oscillator.
DESCRIPTION OF REFERENCE NUMERALS AND SIGNS
60 OSCILLATOR (OSCILLATOR A) 61 OSCILLATION START UNIT 63
OSCILLATOR (OSCILLATOR B)
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment
An ultrasonic flowmeter in a first embodiment of the invention
comprises an oscillator and an oscillation start unit for
accelerating oscillation of the oscillator, and is constructed so
as to use a pulse of the oscillator oscillated by the oscillation
start unit in measurement of propagation time of ultrasonic
waves.
FIG. 1 is a circuit block diagram showing a configuration of the
ultrasonic flowmeter in the first embodiment of the invention.
In FIG. 1, a flow path 50 is a pipe through which fluid flows, and
ultrasonic sensors 51, 52 are disposed on the way. The ultrasonic
sensors 51, 52 are connected to a printed substrate in which a
control part 53 is disposed by lead wires. The control part 53 made
by having a sending circuit 54 for supplying a sending signal to
the ultrasonic sensors 51, 52, a receiving circuit 55 for
transmitting a signal from the ultrasonic sensors 51, 52, an
amplification circuit 56 for amplifying an output of the receiving
circuit 55 and a comparison circuit 57 for comparing an output of
the amplification circuit 56 with a DC voltage is disposed in the
printed substrate.
A switch group 58 is disposed in order to switch between sending
and receiving of the ultrasonic sensors 51, 52, and is in a state
in which the ultrasonic sensor 51 is connected to the sending
circuit 54 and the ultrasonic sensor 52 is connected to the
receiving circuit 56 in FIG. 1. A calculation processing circuit 59
transmits a sending command to the sending circuit 54 and drives
the ultrasonic sensor 51. When the ultrasonic sensor 52 receives
ultrasonic waves sent from the ultrasonic sensor 51, its received
signal is processed by the receiving circuit 55 and the
amplification circuit 56 and a signal is outputted from the
comparison circuit 57.
The signal from the comparison circuit 57 is transmitted to the
calculation processing circuit 59, and the calculation processing
circuit 59 measures time taken to transmit the signal from the
comparison circuit 57 from sending of the ultrasonic sensor 51. In
this time measurement, pulses formed by an oscillator 60 are used
and the number of pulses during a propagation period of ultrasonic
waves is counted and time is calculated. Here, as an oscillation
frequency of the oscillator 60, for example, the oscillation
frequency of 4.times.10.sup.6 Hz (0.25.times.10.sup.-6 second) is
selected. The oscillator 60 is energized by an oscillation start
unit 61. The oscillation start unit 61 is configured to have
another oscillation unit 62 and a circuit for energizing pulses of
this oscillation unit 62 to the oscillator 60 for a certain
period.
This another oscillation unit 62 is unit of generating a pulse with
a frequency substantially equal to a frequency of the oscillation
unit 60, and is constructed of a ring oscillator since it is
desirable to generate a pulse instantaneously. Since frequency
accuracy of the ring oscillator is not good, the ring oscillator
cannot be used in measurement, but the ring oscillator can be
utilized sufficiently for the purpose of energizing the oscillator
60 and accelerating an oscillation start of the oscillator 60 and
accelerating stability of duty or an oscillation frequency.
A method for accelerating an operation start of an oscillator using
such a ring oscillator is described in, for example, U.S. Pat. No.
6,819,195B1. The same patent is a method for energizing an
oscillator while adjusting a frequency of a ring oscillator, and we
confirm that such a method has an effect of accelerating stability
of a pulse cycle.
Incidentally, other methods for reducing time taken to enable the
pulse to be used from activation of an oscillator are introduced.
For example, JP-A-11-163632 of Japanese Patent is not a method for
energizing an oscillator, so that it is undesirable since an effect
of accelerating stability of a pulse cycle cannot be expected even
when time to a pulse output is reduced.
According to the first embodiment thus, by disposing the
oscillation start unit 61, an oscillation start of the oscillator
60 used in measurement of propagation time of ultrasonic waves by
the ultrasonic sensors 51, 52 can be accelerated and stability of
an oscillation pulse can be enhanced. Consequently, stable
measurement of propagation time of ultrasonic waves can be started
instantaneously, so that high-accuracy measurement can be made
intermittently and electric power savings in the ultrasonic
flowmeter can be achieved.
Second Embodiment
An ultrasonic flowmeter in a second embodiment of the invention is
constructed so that a driving signal is given to an ultrasonic
sensor in synchronization with a pulse of an oscillator oscillated
by an oscillation start unit and a waiting period is disposed until
the driving signal is given to the ultrasonic sensor after being
oscillated by the oscillation start unit.
FIG. 2 is a timing chart of the ultrasonic flowmeter in the second
embodiment of the invention, and represents signals of places of A,
B, C, D, E and F described in FIG. 1. B of FIG. 2 is a signal from
the calculation processing circuit 59 and is a signal for
operation/stop of the oscillator 60. C of FIG. 2 is similarly a
signal from the calculation processing circuit 59 and is a signal
for defining a period for which the oscillator 60 is energized by
pulses of another oscillation unit (ring oscillator) 62. A of FIG.
2 is a pulse signal of this another oscillation unit (ring
oscillator). D of FIG. 2 is a pulse signal of the oscillator 60,
and the instant that energization from this another oscillation
unit (ring oscillator) is stopped, a pulse waveform is somewhat
disturbed, but a normal pulse is outputted at once.
E of FIG. 2 is a driving signal of the ultrasonic sensor 51 and the
driving signal is generated in synchronization with a pulse signal
D of the oscillator 60 of D of FIG. 2. F of FIG. 2 is a signal
outputted by the comparison circuit 57 based on a signal received
by the ultrasonic sensor 52. The instant that energization from
this another oscillation unit (ring oscillator) is stopped, a pulse
waveform is somewhat disturbed by a pulse signal of the oscillator
60 of D of FIG. 2, so that time is somewhat required in order to
stabilize a pulse frequency. As a result of this, waiting time T is
disposed between the signal and the driving signal of the
ultrasonic sensor 51 of E of FIG. 2 outputted in synchronization
with the pulse signal D of the oscillator 60 of D of FIG. 2.
When a ceramic oscillator is used in an oscillator, waiting time is
about 30.times.10.sup.-6 second. In FIG. 2, time TT represents
propagation time of ultrasonic waves and also, time TF represents
time for which the oscillator 60 is energized. Since time TF+TT
taken to energize the oscillator 60 and output a driving signal is
about 50.times.10.sup.-6 second, as described in the section of
"Problems that the Invention is to Solve", with respect to the fact
that "when the ceramic oscillator is used, activation of the
oscillator becomes extremely quicker than that of the crystal
oscillator, but about 200.times.10.sup.-6 second or more is
required still, so that a problem is to accelerate activation of
the ceramic oscillator further in order to achieve electric power
savings", time can be further reduced to about one-fourth.
According to the second embodiment thus, by disposing the waiting
time T until the driving signal is given to the ultrasonic sensors
51, 52 after being oscillated by an oscillation start unit 61, a
stable operation can be performed as soon as possible in the case
of accelerating an oscillation start of the oscillator 60 by
energization of another oscillation unit 62.
Third Embodiment
An ultrasonic flowmeter in a third embodiment of the invention is
constructed so that other oscillator B is disposed in addition to
an oscillator A used in measurement of propagation time of
ultrasonic waves and a pulse cycle of the oscillator A is verified
by a pulse of the oscillator B to calibrate propagation time.
FIG. 3 is a circuit block diagram showing a configuration of the
ultrasonic flowmeter in the third embodiment of the invention, and
the circuit block diagram of the ultrasonic flowmeter shown in FIG.
1 is simplified and a part is added. In FIG. 3, an oscillator 60
which is the first oscillator A is used for measuring propagation
time of ultrasonic waves and as its oscillation frequency, for
example, the oscillation frequency of 4.times.10.sup.6 Hz is
selected. This oscillator 60 performs intermittent operations and
is energized by an oscillation start unit 61 at the time of an
oscillation start. An oscillator 63 which is the second oscillator
B is an oscillator for generating pulses to form the basis of an
operation of a calculation processing circuit 59 and as its
oscillation frequency, for example, the oscillation frequency of
32.times.10.sup.3 Hz is selected. This oscillator 63 performs
continuous operations.
This oscillator 63 is used for a microcomputer constructing the
calculation processing circuit 59 and the frequency is low, so that
power consumption is small but at such a frequency, a cycle is too
long and the oscillator 63 is not used in measurement of
propagation time of ultrasonic waves directly.
In the oscillator 60 which is the oscillator A, a ceramic
oscillator is used. In the oscillator 63 which is the oscillator B,
a crystal oscillator is used. As described above, frequency
accuracy is .+-.0.5% in the ceramic oscillator while frequency
accuracy is .+-.0.001% in the crystal oscillator, so that the
frequency accuracy of the ceramic oscillator is not sufficient for
high-accuracy measurement. As a result of this, the ceramic
oscillator (oscillator A) is verified by the crystal oscillator
(oscillator B). The verification is performed so that as shown in
FIG. 4, the number of pulses of the ceramic oscillator (oscillator
A) of (b) in FIG. 4 per one cycle TA or plural cycles of the
crystal oscillator (oscillator B) of (a) in FIG. 4 is counted and
time per one cycle of the ceramic oscillator (oscillator A) is
obtained and propagation time of ultrasonic waves obtained by the
number of pulses of the ceramic oscillator (oscillator A) is
corrected by its value.
According to the third embodiment thus, the ceramic oscillator with
quick activation is used in the oscillator A for measurement of
propagation time of ultrasonic waves and the crystal oscillator
with high oscillation frequency accuracy is used as the oscillator
B and a pulse cycle of the oscillator A is verified by a pulse of
the oscillator B and thereby, stable measurement of propagation
time of ultrasonic waves can be executed instantaneously.
Fourth Embodiment
A fourth embodiment is constructed so that verification of a
ceramic oscillator (oscillator A) by a crystal oscillator
(oscillator B) is performed continuously after measurement of
propagation time of ultrasonic waves. FIG. 5 is a timing chart of
an ultrasonic flowmeter in the fourth embodiment of the invention,
and (a) in FIG. 5 shows an operation of an ultrasonic sensor A, and
(b) in FIG. 5 shows an operation of an ultrasonic sensor B, and (c)
in FIG. 5 shows an operation of the oscillator A.
In order to obtain pulse stability after time TF for which the
ceramic oscillator (oscillator A) is energized, waiting time T is
taken and sending 64 is performed from the ultrasonic sensor A. A
signal of the ultrasonic sensor A is received 65 by the ultrasonic
sensor B and propagation time TT of ultrasonic waves is measured.
Thereafter, the ceramic oscillator (oscillator A) is stopped for
time TS.
The ceramic oscillator (oscillator A) is again energized for time
TF and after waiting time T, sending 66 is performed from the
ultrasonic sensor B. A signal of the ultrasonic sensor B is
received 67 by the ultrasonic sensor A and propagation time TT' of
ultrasonic waves is measured. Thereafter, the ceramic oscillator
(oscillator A) operates continuously for time TC in order to
perform verification of the ceramic oscillator (oscillator A) by
the crystal oscillator (oscillator B).
In the fourth embodiment thus, by performing verification
continuously without stopping the ceramic oscillator (oscillator
A), it is unnecessary to again energize the ceramic oscillator
(oscillator A) and take the waiting time, so that electric power
savings can be achieved.
Fifth Embodiment
A fifth embodiment is constructed so that waiting time taken to
obtain pulse stability after the ceramic oscillator (oscillator A)
described above is energized is given as a constant time. Since the
time taken to obtain pulse stability varies depending on variations
in characteristics between individual pieces of the ceramic
oscillators or temperature, time necessary for stability including
these factors is previously measured and the waiting time is given
as a fixed value in a range capable of sufficiently covering these
factors.
By this configuration, the waiting time can be set the most simply,
so that a software scale or a circuit element scale of a
calculation processing circuit can be reduced.
Sixth Embodiment
A sixth embodiment is constructed so that waiting time is
determined by verifying a pulse cycle of an oscillator. That is,
during the waiting time during which pulse stability is waited
after a ceramic oscillator (oscillator A) is energized, a cycle of
the ceramic oscillator (oscillator A) is verified by a crystal
oscillator (oscillator B) and it is decided that the pulse
stability of the ceramic oscillator (oscillator A) is obtained when
a verification error is within a certain range based on a
verification result.
According to this configuration, a software scale or a circuit
element scale of a calculation processing circuit for setting the
waiting time becomes large, but there is an advantage capable of
properly setting the waiting time.
The invention has been described in detail with reference to the
particular embodiments, but it is apparent to those skilled in the
art that various changes or modifications can be made without
departing from the spirit and scope of the invention.
The present application is based on Japanese patent application
(patent application No. 2006-351251) filed on Dec. 27, 2006, and
the contents of the patent application are hereby incorporated by
reference.
INDUSTRIAL APPLICABILITY
As described above, an ultrasonic flowmeter according to the
invention can be expanded into uses of a business or household
ultrasonic type gas flow rate measuring apparatus (gas meter) for
measuring a flow rate of natural gas or liquefied petroleum gas
requiring accurate measurement.
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